Make sure you make a deck between 60-65 cards because you wont get the cards you want. If you make a 80-100 card deck, and you had 40 mana at the bottom of your deck, and 40 other at the top, you will lose the game when you shuffle your deck and play. Its a 50/50 chance next turn you'll get the card you want. Be smart with building a deck. You want 25-30 mana, 20 creatures, and 10 enchantments/artifacts/instants. Always figure out mana and creatures first, then do other stuff to your deck...

A big problem for many starting players is Mana. You need a deck with just enough mana. You're doomed if you don't get your lands or other Mana cards, but you're no better off if you get only Mana and no Creatures or other Spells. It has to be balanced. A little more than 1/3 of your deck should be Mana. When you use a 60 card deck, 24 mana will suffice, but at the very least one land for every two spells.

Another problem many starters have is that they don't get the right color of mana. If you have too many different colors in your deck, the chance that you'll draw the right color reduces. Therefore, it is better to create a deck with 1, 2 or maybe 3 different colors. Decks with 4 colors, and even all 5, can work as well, but a starter should keep it to a maximum of 3. If you want, you can always add Artifacts or multi-color Spells to your deck.

The balance between the number of Creatures and other spells varies from deck to deck, but you always need creatures, and enough of them. You also want Sorceries, Instants and other Spells to help destroy your opponent's life total and creatures, control their cards, enhance your creatures and more. Creatures are there to defend you from your opponent's creatures and attack your opponent, and can often be sacrificed for other Spells. Keep them balanced. Most people have more creatures than Spells in their deck.

Some Ideas for a Beginner Deck: Here are some categories that you can base your deck off of:Edit